External Monitor on DELL 9430

Hi 

I have recently bought the DELL 9430 2-in-1 (with absolute top line specs). I had the previous model before. The problem did not occur on the previous model but only on the new model.

The problem:

I have a LG 27QP88d-p monitor, I connect the first monitor with USB-C by plugging in the USB-C cable of the monitor into my Laptop. The first monitor (DP Out) is then daisy chained with the second monitor (DP in) via DP. I have my keyboard, webcam and my mouse connected to the first monitor, they work. The USB-C is also charging my laptop. But the monitor doesn´t get any signal. The monitor has USB-C as an input defined. I did not make any changes compared to the setup before.  

With my old laptop (basically exactly the same as the new one, just three years older), everything worked liked a charm. Now I am not getting this to work. 

A docking station is no option, anyhow, as it worked before, it should not be an issue of that. 

Maybe someone has a good idea.